Characteristics And Geological Dynamic Response Of Coalbed Methane Reservoir In Jixi Mining Area

This thesis aims at the mining panels in Xinghua and Donghai Mine in Jixi mining area,the characteristics of CBM reservoirs in the study area is summarized,the development potential of gas-bearing units based on the planned coal mining panels is analyzed,the coalbed methane development unit in the mining area is optimized,the geological dynamic response characteristics under mining disturbance are analyzed by numerical simulation,and the best well distribution area of surface well in mining panels is studied.The productivity characteristics of CBM surface wells in the mining area are summarized,and the effects of pressure relief range and negative pressure of extraction on the productivity of surface wells in the mining area are explored.The vitrinite content of the coal seam in the study area is 76.8?88.35%,and the vitrinite reflectance is 0.90?1.08%,which belongs to gas coal or 1/3 coking coal.The pores of the coal seams in the north of the mining area are mainly large pores,while the pores of the coal seams in the south are mostly small pores.The test results show that the coal seam in Xinghua mine only has open pores in the mesopore,while most of the pores of other sizes are closed pores.Microscopic observation shows that the pore shape of Xinghua Coal seam is mainly stomata,and some brecciate pores and broken grains can be seen,while the fracture morphology is mainly pressure fractures of endokinetic fractures,and a few static pressure fractures of exogenetic fractures can be seen.The connectivity and gas conductivity of coal reservoir are poor in general.The calculation range of the gas-bearing unit in the mining panels of the study area is determined,the evaluation index system of coalbed methane development potential in mining area is established,the development potential of the gas-bearing unit is evaluated to select the development units for the CBM extraction by surface wells in the mining area.The results show that the left 2^nd panel of 28#in the first mining area of Xinghua Mine and left 9^th panel of 34#in the sixth mining area of Donghai Mine have high development potential.The geological dynamic response characteristics of the mining disturbance is analyzed by numerical simulation.It is concluded that the areas with large horizontal displacements are distributed in a"saddle shape"along the dip,and the areas with severe vertical tension and compression are distributed in a"parabolic shape"along the dip.The maximum shear stress gradually increases with the excavation of the working face,and the response characteristics of the maximum principal stress have a greater relationship with the combination of soft and hard rock formations in the fracture zone.Based on the dynamic response characteristics of stress and displacement,considering the extraction effect,the advantageous well layout area was obtained,which guided the well location deployment of Well HJD4.Well HJD4 operated 197 days in total,pumping 3.193×10⁶ m³ of pure methane.When the working face is advanced to 55 m from the bottom of the borehole,no methane is pumped in the wellbore,and when it is advanced to 20 m from the bottom of the borehole,the methane concentration rises significantly to more than 90%,and the pressure relief of mining can greatly increase the permeability of the CBM reservoir.When the working face is advanced to more than 90 meters through the bottom of the hole,the well in the mining area can still maintain stable and high production for a long time,and the permeability reduction caused by re-compaction is small under the condition of lower mining height.The necessity of maintaining continuous and stable mining at the working face for the stable and high production of wells in the mining area is clarified,and the reason for the low gas production caused by the high suction negative pressure in Well HJD4 is revealed.This thesis has 59 figures,31 tables and 96 references.